Making flexible detonating fuse



Sept. 10, 1968 TING F Original Filed Aug 19, 1960 3,401,215 MAKINGFLEXIBLE DETONATING FUSE William L. Evans, Blackwood, N.J., assignor toE. I. du Pont de Nemours and Company, Wilmington, Dei., a corporation ofDelaware Original application Aug. 19, 1965, Ser. No. 481,150, nowPatent No. 3,338,764, dated Aug. 29, 1967. Divided and this applicationMay 2, 1967, Ser. No. 651,062

7 Claims. (Cl. 2643) ABSTRACT OF THE DISQLOSURE A detonating fuse madeby intimately mixing a capsensitive particulate high explosive; acopolymer of a butadiene, an acrylonitrile and a suflicient amount of anacrylic acid to provide from about 0.001 to 0.3 carboxyl equivalent per100 parts said copolymer, a source of polyvalent metal ion andplasticizer, heating the mixture to form a metallocarboxylate elastomer,forming the composition into a predetermined shape, e.g. extrudingaround reinforcing element, and curing the detonating fuse at roomtemperature or above.

This application is a division of application Ser. No. 481,150, filedAug. 19, 1965, now Patent 3,338,764.

This invention relates to novel explosive compositions, to flexible,shaped, detonatin-g articles made from said compositions, and to methodsfor manufacturing such compositions and articles.

Flexible detonating fuses have been widely employed as priming agents,as conveyors of detonation, generators of shock pressure, and the like,both in commercial and in military applications. Thus, one of the firstwidely used and practically effective articles of this kind was adetonating fuse known under the name Cordeau (US. Patent No. 869,219)which consisted of a metal tube, generally of lead or lead alloy, filledwith trinitrotoluene. This fuse, however, was relatively low in tensilestrength, especially in small diameters; was easily deformed orfractured by mild impacts and by bends because of its low order ofresilience, toughness and tensile strength; was relatively heavy perunit of length; was relatively low in initiating power because of themetal sheath surrounding the explosive core; could not be used aboveabout 175 F. because the explosive core melted and became lesssensitive; and was expensive to manufacture.

An effective successor to Cordeau is a detonating fuse which consists ofan explosive core of PETN (pentaerythritol tetranitrate) containedwithin a waterproofed textile covering or a textile and plasticcovering, these assemblies for a given length of detonating fuse beingabout one-fifth as heavy as the same length of Cordeau. Commerciallyavailable forms of this detonating fuse are well known. They have muchgreater tensile strength than Cordeau fuse, better resistance todeformation, are relatively easy to handle and use, and have a highervelocity of detonation and better priming power. At a considerableincrease in cost, detonating fuse having even higher tensile strengthcan be obtained by applying 'metal wire wrapping over the fabriccovering. The flexibility of the fabric-covered cord, however, isinadequate for satisfactory use at temperatures below about 40 F., andthe flexibility is even further impaired by the presence of reinforcingwire coverings. Although PETN, the explosive core, is not soluble inwater and absorbs water very slowly, the above described fabriccovered,PETN-containing, detonating fuse is not completely waterproof; forexample, wet ends may lead to priming failures, and failure ofpropagation of detonation nited States Patent ice to branch lines mayoccur if water penetrates at knotted connections where the waterproofingcover is broken. Furthermore, knotted connections may cause failures ofpropagation unless the branch line is at an angle greater than about 30from the main line in the direction of detonation.

Flexible detonating compositions, as well as shaped articles containingsuch compositions, also have become available in recent years in theform of sheets, cords, and other shaped masses as disclosed in US.Patents Nos. 2,992,087, 2,999,743, 2,965,466, 2,999,744, 3,018,201 and3,116,186. These detonating compositions generally comprise acap-sensitive explosive held in a matrix of one of several polymericbinders, incorporation of which requires exothermic fluidpolymerization, relatively high temperature curing, or incorporation involatile, toxic or flammable solvents which subsequently are removed;all processes which are unattractive from the standpoint of safety inmanufacture, and generally give products which lack flexibility at lowor subzero temperatures, or have limited toughness at ordinarytemperatures, said toughness being further reduced at elevatedtemperature. These deficiencies in physical properties are especiallyapparent, for example, in the ease with which the compositions are cutthrough by reinforcing members under tension, in the significant loss oftensile strength as temperatures of the compositions increase from roomtemperature to 140 F. or even higher, and in the brittleness which isapparent at temperatures of 0 F. and lower. The manufacturing proceduresemployed and some of the binders used in the explosive compositions areinherently expensive to the point of resulting in flexible productswhose limited special properties are attained only at a considerableeconomic penalty.

The potential utility of shaped explosive articles comprisingparticulate cap-sensitive detonating explosives in a natural orsynthetic rubber matrix was disclosed in US. Patent 2,067,213, andmethods of manufacturing the compositions by incorporating thecap-sensitive high explosives in water-bearing rubber latices also weredisclosed. Such compositions and the articles made from them, however,were not suitable for general use over the wide range of temperaturesencountered under normal conditions of use in the explosive industrybecause the articles lost their flexibility and became stiff and brittleat relatively low temperatures, of the order of 0 F., and lackedsufficient tensile strength for satisfactory use at the higher end ofthe temperature range, e.g., about 120 F. As a result, detonating tapes,sheets, cords and trains made from such compositions were not generallyadopted for use in the industry.

An object of the invention is to provide a commercially feasible andeconomical method for making explosive compositions and also forfabricating the compositions into various shapes for subsequent use.

It has now been discovered that novel explosive compositions areobtained by intimately mixing a polymeric carboxylic elastomer that is acopolymer of from about 50 to percent by weight of a butadiene, fromabout 10 to 45 percent by weight of an acrylonitrile and a suflicientamount of an acrylic acid to provide from about 0.001 to 0.3 carboxylequivalent per parts by weight of said copolymer; a source of polyvalentmetal ions in an amount chemically equivalent to about 0.5 to 2 timesthe carboxyl con-tentof the copolymer; from about 1 to 20 percent byweight of a plasticizer; and from about 40 to 80 percent by weight of aparticulate cap-sensitive high explosive. Preferably, but optionally, upto 25 percent by weight of a liquid polyurethane elastomer is added tothe explosive composition in order to obtain optimum physical propertiesin relation to flexibility.

Thus, the novel elastomer-bonded explosive composition of the presentinvention comprises an intimate uniform mixture of from about 40 to 80percent by weight of a cap-sensitive particulate high explosive, fromabout to 50 percent by weight of a polymeric metallocarboxylateelastomer and from about 1 to percent by weight of a plasticizer for thecarboxylate elastomer. The polymeric metallocarboxylate elastomer is thereaction product of a polyvalent metal ion, which acts as a curing agentfor the elastomer, with a copolymer of from about 50 to 80 percent byweight of a butadiene, from about 10 to 45 percent by weight of anacrylonitrile and a sufiicient amount of an acrylic acid to provide fromabout 0.001 to 0.3 carboxyl equivalent per 100 parts of said copolymer,the polyvalent metal ion being present in an amount chemicallyequivalent to about 0.5 to 2 times the carboxyl content of saidcopolymer. Most preferably, the explosive composition contains up toabout percent by weight of a polyurethane elastomer. However, the amountof polyurethane, if used, should generally not exceed about the amountof metallocarboxylate elastomer.

The resultant explosive composition is flexible and can be formed into avariety of shapes that retain substantially the dimensions and form intowhich the compositions are fabricated. For example, the explosivecompositions can be shaped by pressing into blocks, slabs or sheets, byrolling into sheets and films, and by extruding into rods, cords, tubesor sheets. The shaped articles are flexible, yet have a desirable hightensile strength. These explosive compositions have been found to beparticularly useful and supply a long sought after need in the explosiveindustry, especially when formed into tubes, tapes and cords which canbe produced by, for example, continuous rolling or extrusion operations.It has been found that explosive cord, or as it is more commonlyreferred to in the industry, detonating fuse, fabricated from the novelexplosive compositions, and preferably, but not necessarily, containinga reinforcing element and a polyurethane elastomer, greatly increasesthe uses and conditions under which detonating fuse operateseffectively. For example, flexibility and strength of the detonatingfuse of this invention are retained to such an extent that thecompositions and articles of the invention are useful over a temperaturerange of from about 50 F. to 180 F.

In relation to detonating fuse, any reinforcing element that iscompatible with the explosive composition can be used. Optimum physicalproperties as to flexibility and tensile strength are obtained when theexplosive composition is formed into an elongated or cord-shaped fuse,and yarn, particularly nylon yarn, is employed as the reinforcingelement which is substantially centrally positioned within the fuse andalong its longitudinal axis.

In order to more fully describe a preferred embodiment of a detonatingfuse and its method of preparation, reference is made to the singlefigure in the drawing illustrating one means for manufacturingdetonating fuse.

The drawing illustrates a cross sectional view of an apparatus forextruding the explosive composition around a central reinforcing memberin order to make a reinforced detonating fuse, which is a preferredembodiment of the invention. The apparatus comprises a ram type extruder10 and a barrel 12, a ram 11 at one end of extruder 10 and a formingmeans comprising a die 15 at the other end of the extruder. Thecarboxylate elastomer-containing explosive 18 is added to barrel 12 ofextruder 10. Reinforcing means 17, e.g., nylon yarn is fed from asource, not shown, into a channel in guide member 13, through guideinsert 14 into the explosive composition. In operation, when pressure isapplied to the ram 11, provided with 0 type sealing rings 16, it thusforces the explosive composition through die 15 while the reinforcingelement is simultaneously fed through guide 13 and guide insert 14 at apredetermined synchronized rate into the explosive composition thusforming detonating fuse 19. The

' 4 detonating fuse may be wound on a spool, or other suitable means,for storage.

After the detonating fuse has been formed, e.g., extruded, it is cured.Curing is merely the completion of the reaction between the polyvalentmetal ion and the carboxylic elastomer and can take place at roomtemperature during storage. However, heating the'detonating fuse attemperatures below the decomposition temperature of the particulatecap-sensitive high explosive greatly reduces the curing time. Aconvenient curing temperature being of the order of 160 to 225 F. andfrom about 8 to 24 hours. I I

High explosives suitable for use in the present invention includeparticulate cap-sensitive materials which are stable under theprocessing conditions, which are compatible with other ingredients ofthe compositions, and which are not dissolved by other components of themixtures. The cap-sensitive particulate high explosive constitutes 40 topercent by weight of the explosive composition. Representativecap-sensitive high explosives that can be used are trinitrotoluene(TNT), pentaerythritol tetranitrate (PETN), trinitrophenylmethylnitramine (tetryl), cyclotrimethylenetrinitramine (RDX)cyclotetramethylenetetranitramine (HMX), mannitol hexanitrate,tetranitrodibenzo 1,3a,4,6a-tetraazapentalene, diazidodinitrophenol,hexamethylene triperoxydiamine, picrylsulfone, potassiumdinitroacetonitrile, and lead azide. PETN, tetryl, and RDX are thepreferred cap-sensitive explosives of the composition, and especiallypreferred for general use is PETN. The particle size of the highexplosive is not critical to the success of the invention, althoughparticles all of which pass an SO-mesh U.S. standard sieve arepreferred, and especially preferred are particles whose major dimensionon the average does not exceed microns. The latter are designated hereinas superfine explosives. Generally, the compositions are more sensitiveto initiation if they contain a very fine crystalline cap sensitiveexplosive. The particulate, cap-sensitive high explosive may be dry whenadded for incorporation into the mixture or it may be wet with water,since water is a major component in the latex of the reaction mixture.Use of water-wet high explosive adds to safety in the manufacturingoperation since the water acts as a desensitizer until the explosive isthoroughly incorporated with the carboxylic elastomer and plasticizer,after which the water is removed, for example, by heat and vacuum.

Any plasticizer for the carboxylic copolymer of the explosivecomposition can be used. Incorporating from about 1 to 20 percentplasticizer by weight assists in providing low temperature flexibilityfor the explosive composition. Plasticizers which are particularlysuitable for use either alone or in combination in said compositions areesters and include, for example, triethyleneglycol-di-Z-ethylhexoate,di-n-butyl phthalate, tricresyl phosphate, acetyl tributyl citrate,isodecyloctylphthalate, di-isodecyl adipate, di-isooctyle adipate,dioctyl adipate, dioctyl sebacate. Particularly preferred plasticizersare di-n-butyl phthalate and triethyleneglycol di-2-ethylhexoate whichmay be used either alone or in combination. Other plasticizers which maybe used include, for example, di(butoxyethoxyethyl)formal,tris(,B-chloroethyl)phosphate, and highly aromatic oils such as MobilsolN, Picco 25, and Dutrex 1739. Preferably these will be used incombination With one of the organic ester type plasticizers named above.

Carboxylic elastomer-s which are suitable for manufacture ofcompositions and articles of this invention and constitute the majorportion of the binding matrix thereof are copolymers formed from abutadiene-l,3-hydrocarbon, an acrylic nitrile, and an acrylic acid.Typical butadiene-l,3-hydrocarbons used in preparing said copolymersare, for example, butadiene-1,3 and the 5 to 9 carbon atom homologuesthereof such as isoprene, 2,3-dimethyl butadicue-1,3, pentanediene-1,3,hexadiene-1,3 and mixtures thereof. As used herein, the term acrylicnitrile refers to acrylonitrile and alpha-substituted acrylonitriles,that is, compounds having the formula:

Examples of acrylic nitriles are acrylonitrile, methacrylonitrile,ethacrylonitrile, alpha-butylacrylonitrile, alphaphenyl acrylonitrile,alpha-chloroacrylonitrile and alphamethoxymethyl acrylonitrile andmixtures thereof.

Carboxyl groups are introduced into the copolymers by copolymerizing theaforementioned butadiene-1,3-hy drocarbons and acrylic nitriles with atleast one acrylic acid. Copolymers containing about from 0.001 to 0.3,and preferably 002 to 0.15, carboxyl equivalent of at least one acrylicacid per 100 parts by weight of copolymer are preferred. As used hereinthe term carboxyl equivalent of an acrylic acid refers to the amount ofthe chemically combined acrylic acid which contains one equivalentweight, that is, 45 parts by weight of free carboxyl groups. The amountof free carboxyl groups in a given copolymer can be determined bytitrating a solution of the carboxylicmodified copolymer with alcoholicpotassium hydroxide to a phenolphthalein end-point. As used herein, theterm acrylic acid refers to acrylic acid and alpha-substituted acrylicacids, that is, compounds having the structural formula:

Acrylic acids which are copolymerized with butadiene- 1,3-hydrocarbonsand acrylic nitriles thereby introducing free carboxyl groups into thecopolymers are, for example, acrylic acid, methacrylic acid, ethacrylicacid and alpha-chloro acrylic acid. Copolymers of from 50 to 80% byweight of a butadiene and from about to 45% by weight of anacrylonitrile containing from about 0.001 to 0.3, and especially 0.02 to0.15, carboxyl equivalent of an acrylic acid per 100 parts by weight ofcopolymer are preferred. Especially preferred carboxylic copolymers foruse in making articles of the present invention are made frombutadiene-1,3, acrylonitrile, and methacrylic acid.

Although said copolymers may be incorporated into the explosivecomposition by first dispersing them in volatile organic solvents suchas aliphatic hydrocarbons, halogenated aliphatic hydrocarbons, toluene,or methyl ethyl ketone, the preferred form of the copolymers is a latexcontaining from about 3560% of solids dispersed in an aqueous medium.Such latices present several advantages since latices are the form inwhich said copolymers are made and, therefore, represent the lowest costform of the copolymers; no costly and hazardous organic solvents arerequired to fabricate the articles of this invention; and finally thepresence of Water in the latex greatly increases the safety of mixingoperations wherein a cap-sensitive particulate high explosive isincorporated with the copolymer, the plasticizer, and the source ofpolyvalent metallic ion. During mixing the reaction mixture may beheated to slowly remove the water or solvent.

Several grades of said butadiene-1,3, acrylonitrile, methacrylic acidcopolymers may be made, depending upon the ratios of the monomericmolecules which are incorporated in the copolymer. Generally these aredescribed as high, medium, or low acrylonitrile copolymers depending onthe proportion of acrylonitrile incorporated in the copolymer, e.g.,5035%, 35-17%, and l71%, respectively for high, medium, and low; and arefurther characterized by the carboxyl content of the copolymer, asindicated above. For manufacture of articles of the present invention,latices of copolymers of intermediate acrylonitrile content, andcarboxyl (-COOH) content of 0.02 to 0.15 part by weight per 100 parts ofcopolymer, are preferred. Such latices are commercially available as,for example, Hycar 1570X20, 1570X36, 1571 and 1572 (made by the B. F.Goodrich Chemical Co.), of which Hycar 1572 is especially suitable. Suchcommercially available copolymer latices may be used alone, or incombination with one another or in combination with polyurethaneelastomers in order to obtain the physical properties desired in thefinished compositions. Adjustments of compositions, curing agents andprocessing conditions to obtain desired physical properties is wellknown in elastomer technology and is regularly practiced by thosefamiliar with elastomer art.

Any source of polyvalent metal ions can be used as a curing agent forthe carboxylic copolymer. Polyvalent metal oxides, hydroxides andother'sources of polyvalent metal ions such as salts of an acid weakerthan acetic acid, and salts of an acid readily eliminated from thecrosslinking site, and even finely divided metals, are compounded with,and are used to cure, said carboxylic copolymers by formingcorresponding metallocarboxylate. Representative examples of such metaloxides and other sources of polyvalent metal ions are, for example, zincoxide, calcium oxide, magnesium oxide, dibutyltin oxide, lead oxide,barium oxide, cobalt oxide, tin oxide, zinc carbonate, calcium silicate,zinc acetate, sodium aluminate, sodium phosphomolybdate, and mixturesthereof. Zinc oxide is preferred. Usually from about 0.5 to 2 times thechemical equivalent weight of polyvalent metallic oxide, or other sourceof polyvalent metal ion, with respect to the amount of carboxyl group insaid carboxylic copolymer is used in formulating compositions andarticles of this invention.

It can be seen from the above that the metallocarboxylate is thereaction product, formed in situ, between a polyvalent metal ion and acarboxylic copolymer of a butadiene, an acrylonitrile, and an acrylicacid, said copolymer containing from 0.001 to 0.3 carboxyl equivalent ofan acrylic acid for each 100 parts by weight of copolymer, andconstitutes 15 to 50% by weight of the explosive composition. At leastabout 15% of the polymeric metallocarboxylate is required to give thedesired flexibility, abrasion resistance, and tensile strength to thecompositions, but if more than about 50% of said metallocarboxylate ispresent, the sensitivity of the explosive composition may be less thanis desired for effective initiation and propagation of detonation,especially in articles of small cross section or diameter, or acrossjoints between articles. The carboxylic copolymers which are used in thecompositions, and their methods of preparation are described in detail,for example, in U.S. Patents Nos. 2,395,017 and 2,724,707 and arefurther described in A New High-Strength Elastomer, Rubber \Norld 130,784-8 (1954); Carboxylic Elastomers, Industrial and EngineeringChemistry 47, 100612 (1955); and Rubber Chemistry and Technology 28, 937(1955). Preferably, up to about 25 percent by :weight of a polyurethaneelastomer, either a polyether or linear polyester type, is incorporatedin the explosive composition. The addition of a polyurethane elastomeris especially desirable in explosive compositions which are to be shapedinto detonating fuse. Liquid polyurethane elastomers which arecharacterized by having reactive isocyanate groups by which said liquidpolymers can be cured to form solid elastomers, as is well known in theart pertaining to synthetic elastomers, are particularly suitable andare commercially available as, for example, Adiprenes L100, L167, L315,and L-420 which are manufactured by E. I. du Pont de Nemours & Co.

Adiprene L100 is a liquid polyether urethane elastomer which is made byreacting 1 mol of polytetramethylene ether glycol (PTMEG) of numberaverage molecular weight about 1000 with about 1.6 mols of mixedtolylene diisocyanates, as disclosed, for example, in U.S. Patents Nos.2,929,800 or 2,948,691. Adiprene L315 also is a liquid polyetherurethane elastomer and is made by reacting 1 mol of PTMEG of numberaverage molecular weight about 1000, 1 mol of butanediol-l,3 and about 4mols of mixed tolylene diisocyanate isomers for 4 hours at C. undernitrogen, as disclosed in U.S. Patent No. 3,188,302. Such liquidpolyether urethane elastomers sometimes are designated as prepolymers orintermediate polymers because on reaction with curing agents they arecured or vulcanized to form solid elastomers.

Liquid polyurethane elastomers, even when incorporated into compositionsof the invention without added curing agents, do cure to some extent andenhance the toughness of the final explosive composition. Preferably,however, curing agents for the liquid polyurethane elastomers also areincluded in the formulation, as exemplified hereinafter. Said curingagents include diamines, polyols, titanate esters, and others well knownin the art. Diamines arethe best general purpose curing agents, and 4,4methylenebis(Z-chloroaniline), commonly designated MOCA, is preferred.By reaction with said diamine, for example, the liquid polyurethaneelastomer is converted to a cured solid polyurethane elastomer whichforms a part of the rubbery binder matrix of the explosive compositionsand articles of the invention.

The designated carboxylic elastomers and polyurethane elastomers areespecially suitable for the preparation of shaped articles, e.g.,detonating fuse, of the present invention because these polymers can beerosslinked, i.e., vulcanized or cured, at temperatures much lower thanthose employed with other elastomers. Curing may be achieved even atroom temperature, but preferably is accomplished in a shorter time atelevated temperatures. The temperature chosen will be regulated by thethermal stability of the explosive-containing mixture which is beingcured, and, of course, curing temperatures are less than the thermaldecomposition temperature of the cap-sensitive explosive. Thus, forexample, a temperature of 200'- 225 F. is convenient for curingPETN-containing compositions. A further advantage associated with use ofsaid elastomers in the products and process of the present invention isthat the commonly used sulfur and sulfurbearing accelerators are notrequired to cure the initially plastic rubbery mixture. Sulfur andsulfur-bearing vulcanization accelerators are incompatible with manycapsensitive explosives, i.e., degradative chemical reactions may takeplace at elevated temperatures of processing and storage. Thus, theadvantages of good cure at relatively low temperatures, freedom from therequirement of milling which is standard practice with conventionalcurable elastomeric materials, and elimination of sulfur andsulfur-bearing curing agents are highly desirable for highexplosives-containing compositions, as in the present invention, and arecharacteristic of elastomers employed in the practice of this invention.

It will be understood that small amounts of other ingredients, ifdesired, may be incorporated in the explosive compositions of thisinvention; for example, stabilizers, pigments and coloring agents foridentification or for increasing visibility, odorants to create apleasant aroma or overcome an objectionable odor of the curedelastomerie binder matrix, antioxidants and retardants.

Useful shaped articles may be formed from the explosive compositions ofthis invention as hereinbefore described, without incorporatingreinforcing means, and the scope of the invention should be understoodto include such articles. For example, the explosive compositions in anuncured or partially cured state may be shaped into blocks, slabs,tubes, sheets, cords, strips or trains and other forms and finish-curedat room or elevated temperatures. Such explosive articles areelastically extensible and find many uses in the explosive field, buttheir utility is greatly increased by including in the article areinforcing means bound to the explosive composition in such manner asto provide an article having great flexibility, even at subzerotemperatures, little extensibility, and much greater tensile strengththan in the absence of such reinforcing means.

The compositions and articles of the present invention, whether theyinclude a reinforcing means or not, are particularly effective and havea high order of utility in the explosives industry because saidexplosive compositions 8 and articles made therefrom are surprisinglyinsensitive to impact and mechanical abuse, they remain completelyeffective after long exposure to water, they require no supplementaryprotective covering for handling, they are nontoxic to users, and incomparison with other explosive compositions used in the industry theyhave enhanced initiating or priming power because of the highconcentration of explosive at the initiation point and the freedom frominert layers of protective covering between initiator and receptorbodies.

Any reinforcing element can beused in'the detonating fuse but yarns andthreads are preferred. Yarns which are suitable for use as reinforcingmeans in the detonating fuse will be selected in accordance with thestrength and performance requirements of the fuse. Such yarns may bemade of cotton, linen, jute, silk, wool, rayon especially high tenacityrayon, cellulose esters, nylon, poly(ethylene terephthalate),polyacrylonitrile, glass or other fibers. Spun fiber yarn constructionusually is preferred to simple monofilament threads since a better bondis established between the spun yarn and the explosive composition ofthe invention. Especially preferred reinforcing means are textured andmultiplex yarns more specificaly described below. It is believed thatthe strength of the bond between the explosive composition and thereinforcing means represents a combination of adhesive and mechanicalinterlocking forces.

Completely satisfactory bond strength is attained when the tensilestrength of the article equals or exceeds the tensile strength of thereinforcing means. That is, a sleeve of the explosive composition in thearticles of the present invention will not strip free of the reinforcingmeans when tension is applied between a portion, for example 12 inches,of the article and exposed extensions of the reinforcing means. Yarnswhich are especially suitable as reinforcing means in the fuse, forexample, a column of said explosive composition containing a centralyarn strand or a multiplicity of yarn strands as the reinforcing means,are textured yarns as described in US. Patent No. 2,783,609 andmultiplex yarns as disclosed in copending and coassigned patentapplication of Field, Ser. No. 397,139, filed Sept. 17, 1964. Texturedand multiplex yarns are preferred for use as reinforcing means becauseof the high inherent tensile strength of said yarns and the firm bondwhich is produced between the yarn and the surrounding sheath ofcap-sensitive high explosive composition.

Textured yarn is defined as a bulky yarn comprising a plurality ofsubstantially continuous filaments which are individually convolutedinto coils, loops, and whorls at random intervals along their lengths,and characterized by the presence of ring-like loops irregularly spacedalong the yarn surface.

A multiplex yarn is defined as a wrapped yarn comprising a core composedof at least two continuous integral core elements of textile fibers andsurface wrappings composed of discontinuous textile fibers, the surfacefibers being tightly twisted about the core with portions of fiberslocked into place in the core, and the core'fibers being relativelystraight and held together as a compact bundle by the surface wrappings.A multiplex yarn in which the continuous core elements are nylon isespecially preferred for use as the reinforcing means in articles of thepresent invention. The gross tensile strength of said multiplex yarn isconveyed to the shaped articles of this invention because of thestrength of binding which is established between said strand ofmultiplex'yarn and the surrounding detonating explosive compositiondescribed herein. For example, use of an 8-ply, 840 denierper-ply,multiplex nylon yarn as the reinforcing means will result in adetonating fuse having a total diameter of about 0.20 inch and a grosstensile strength inexcess-of pounds.

For shaped explosive articles in the form of sheets, individual fibersmay be dispersed in the plastic rubbery explosive mixture beforesheeting out, as by calendering, and curing, or yarns may extendlinearly parallel to the long dimension of the sheet. As an alternate,the sheeted explosive composition may be calendered onto one or bothsides of a latex-impregnated woven fabric or mesh and cured, said wovenfabric or mesh constituting the reinforcing means. Another alternatepermits wrapping reinforcing yarns or threads around an extruded cord ofsaid explosive composition, preferably the surface of said cord iscoated with the aforementioned latex or liquid urethane polymers, andcuring the shaped article. The thread or yarn wrap may be applied as abraided structure over the extruded explosive cord which has beenprecoated with the aforementioned latex or liquid urethane polymer, andthe whole assembly cured by mild heating. Said woven, wrapped, orbraided structure in itself provides the necessary tensile strength forthe article, but the bonding of external reinforcing member to explosivecore is desirable to prevent the covering from unraveling when thearticle, a detonating fuse for example, is cut and to prevent the corefrom slipping out of the external reinforcing means if tension isapplied separately to core and cover. Obviously these methods ofapplying the reinforcing means to the exterior of the shaped explosivecomposition are much more expensive than the aforementioned high speedextrusion of explosive composition about a central reinforcing member ora group of spaced internal reinforcing members. Hence, the use ofinternally placed reinforcing means is preferred in articles of thepresent invention.

Although threads and yarns are preferred as reinforcing means, wire,especially galvanized wire, may be used for this purpose. It is knownthat the aforementioned elastomeric carboxylic copolymers are stronglyadherent to metal and that they can be cured by reaction with freemetals, especially metals which provide a polyvalent ion. Prominentamong these is zinc. Thus, if some free carboxyl groups are available inthe copolymer-bound explosive composition, or the galvanized wire isprecoated with said carboxylic elastomer before being covered by saidexplosive composition, said composition simultaneously cures and adheresto the galvanized iron Wire reinforcing member by reaction between thezinc coating on said wire and carboxyl groups of said carboxylicelastomer. On the other hand, urethane polymers are good adhesivesbetween wire and explosive composition even in the absence of specificsalt-like chemical bonds.

In one effective embodiment of the present invention, the reinforcingmeans is impregnated with a carboxylic clastomer, for example a latex ofthe kind used in making the explosive composition, or a liquid polyetherurethane such as, for instance, Adiprene L-100. Optionally, theelastomer with Which yarns, for example, are impregnated may containplasticizer and curing agents. These promote adhesion between saidreinforcing means and the surrounding composition. A firm bond then isestablished between the reinforcing means and the explosive compositionwith which it is in contact during the curing period which follows theforming or shaping of said articles.

Whatever construction is employed in making articles of this invention,e.g., detonating fuse, the final step in their manufacture is that ofcuring the elastomeric binder matrix and simultaneously binding theexplosive composition to the reinforcing means. Although curing at roomtemperature is known, effective cure can be achieved in shorter times byraising the temperature of the article. Curing at elevated temperaturesis preferred because much less time is required and because abrasionresistance, toughness, and adhesion to the reinforcing means are allincreased. The upper temperature limit for processing, and therebysimultaneously curing the carboxylic copolymer, generally is determinedby the thermal stability of the cap-sensitive explosive ingredient inthe explosive mixture and thus curing temperatures do not exceed thetemperature at which decomposition of the explosive occurs. For example,temperatures of 160-250 F. for 8 to 24 hours are preferred for curingarticles containing PETN, but higher temperatures for shorter times, forexample 8 minutes at 300 F., may be employed with explosives of greaterthermal stability.

The following examples are intended to illustrate the invention further,but not to limit it in any way. Parts and percentages are by weight,unless otherwise specified.

Example 1 Into a jacketed, kneading-type mixer fitted with avacuum-tight cover are charged 55 parts of dry superfine PETN (i.e.,average particle size of PETN is less than 10 microns in maximumdimension), or water-wet PETN containing 55 parts net of PETN; 59 partsof a carboxylic copolymer latex (Hycar 1572) containing about 50% solidsprepared by aqueous copolymerization of about 71.4% of butadiene-1,3,about 28.5% of acrylonitriie, and 0.07% of methacrylic acid; 8 parts ofplasticizer, triethyleneglycol di-Z-ethyl-hexoate; 0.5 part of AgeriteWhite, i.e., di-beta-naphthyl-p-phenylenediamine (an antioxidant); 1.0part of stearic acid; and 6 parts of ZnO. The order of adding theingredients is not critical; however, addition of the particulate highexplosive last is preferred as a somewhat safer procedure. The cover isplaced in position on the mixer, water at about 160 F. is circulatedthrough the mixer jacket, and the agitator is put in motion. After themixer has operated for about 5 minutes, vacuum gradually is applied,with the agitator in motion, until a vacuum of about 29 inches or moreof mercury is achieved, and this is maintained until substantially allwater is removed from the charge in the mixer. The use of vacuum is notnecessary to complete removal of water or solvent, but its use ispreferred because it speeds up processing of the composition. The driedexplosive composition is transferred from the mixer to the barrel orcharging hopper of a ram-type or screw-type extruder fitted with across-head type, circular-orifice die which permits extrusion of theplastic rubbery explosive composition around a multiplex nylon yarnhaving a gross tensile strength of about pounds as it is drawn throughthe die. The barrel and die-head of the extruder are held at from aboutto F. while said composition is being extruded. The multiplex nylon yarnmay contain, for example, 8 ends, each of 840 denier, as hereinbeforedescribed, and be preimpregnated with a carboxylic elastomer. The shapedarticle thereby produced is a partially cured detonating fuse having acentral reinforcing means surrounded by a cap-sensitive detonatingcomposition. The detonating fuse as it is continuously extruded may betaken up on a reel, spool, or other storage means. The partially curedfuse is stored at a temperature of from about 200 to 225 F. for about 8hours when the cure is substantially complete. The fuse has a diameterof about 0.180 inch, is totally unaffected by exposure to water, has agross tensile strength of about 125 pounds, is easily primed by acommercial blasting cap, and detonates at a velocity of about 6568meters/sec. (m./s.). The end of a length of primed detonating fuse wasattached to and initiated a block of pressed TNT. The flexibility ofsaid detonating fuse was demonstrated by holding the fuse at -50 F. forabout one hour and then wrapping said cord around a A in. diametermandrel without fracturing or cracking the detonating cord. Thereinforcing yarn is not stripped from the surrounding detonatingcomposition, even under tension up to rupture, nor does the yarn cutthrough the explosive composition.

Examples 2 to 6 The table below illustrates additional compositionsprepared according to the procedure of Example 1. The

lll

percentages represent the compositionon a dry basis, as charged to themixer.

.12 per-cent by weight of a butadiene, from about 10 to 45 percent byweight of an acrylonitrile and a suflicient Example 2 3 4 5 6 ExplosivePETN PEIN PETN Tetryl RDX Explosive,percent I 55 55 55 5.. H. 75.Carboxylic Copolymer Hyear 1572 Hycar 1572 l'liglgg57z and Hycar 1572.Hycar 1572. G 01 mor ercont 33 (i 2 and 8 20. Pla tigizerjf Dibutylphthalota ol 300 Flexol 300 1 Flexol 300. Plasticizer, percent 8 4.24.1:.

Curing Agent Detonation Velocity, Tensile Strength, 1b.. 1 Low Temp.Flexibility in. mandrel).

1 Flexol 300Triethyleneglycol di-Z-ethylhexoate made by Union CarbideChemicals Co.

Z Reinforcing member was 8 ply, 840 denier/ply multiplex nylon yarn.

Example 7 An explosive composition isprepared as in Example 1 andextruded withouta central reinforcing means. The extruded fuse aftercuring has a diameter of about 0.19 inch and has similar properties tothe cord of Example 1 except that it is elastically extensible at roomtemperature andhas a gross tensile strength at 68 F. of about 15 poundsat rupture. The unreinforced fuse of this example is flexible at 50 F.when tested as in Example 1.

Example 8 The explosive composition prepared according to this examplecontains a liquid polyurethane elastomer. This composition, for example,is particularly well suited for fabrication into detonating fuse whichis to be knotted, as in joining one piece of detonating fuse to anotheror to a high explosive primer, and then subjected to a tensile stress,for example, as in lowering an explosive charge into a borehole.

The procedure employed is substantially the same as that described inExample 1, and the ingredients for the composition are:

Parts PETN superfine 5 8 Hycar 1572 (50% solids) 48.6 Triethylene glycoldi-Z-ethylhexoate 8.0 ZnO 5.0 Antioxidant (Agerite White) 0.5 Liquidurethane polymers 3.0

i.e., polyurethane:

Adiprene L-100 1.0 Adiprene L-3l5 2.0 Methylene-bis(o-chloroaniline)(MOCA) dissolved in about 7 parts of trichloroethylene 0.7 Dyestuff 0.5

Extrusion and curing of the mixed explosive composition in the form ofdetonating fuse of circular cross section and having a nylon yarnreinforcing element are carried out as described in Example 1.

Following the teachings of the invention, a novel explosive compositionis obtained that is flexible and exhibits excellent tensile strengthover a wide temperature range of the order of 50 F. to 180 F.Furthermore, the explosive composition can be formed into a variety ofshapes which retain their dimensions under conditions of use; forexample, flexible, extensible detonating fuse may be made, with orwithout a reinforcing means, that is insensitive to impact and effectiveafter exposure to water for an etxended period. In addition, thereinforcing means of the detonating fuse remains integrally bound to theexplosive composition to prevent any detrimental slippage between saidexplosive and reinforcing means under differential stress up to therupture stress of the reinforcing means.

I claim:

1. A process for manufacturing detonating fuse which comprisesintimately mixing a composition comprising to 80 percent by weight of acap-sensitive particulate high explosive; a copolymer of from about to80 3 Lower flex temperatures are obtained for detonating cords if alarger diameter mandrel is used in the test.

amount of an acrylic acid to provide from about 0.001 to 0.3 carboxylequivalents per 100 parts of said copolymer, and a source of polyvalentmetal ion present in an amount chemically equivalent to about 0.5 to 2times the carboxyl content of said copolymer to provide 15 to 50 percentby weight of a polymeric metallocarboxylate elastomer; .and from about-1 to 20 percent by weight plasticizer, heating the mixture and formingsaid mixture into a predetermined shape and curing at a temperatureabove at least about room temperature and obtaining a flexibledetonating fuse.

2. A process for manufacturing detonating fuse which comprisesintimately mixing a composition comprising 40 to percent by weight of acap-sensitive particulate high explosive; a copolymer of from about 50to 80 percent by weight of a butadiene, from about 10 to 45 percent byweight of an acrylonitrile and a sufficient amount of an acrylic acid toprovide from about 0.001 to 0.3 carboxyl equivalents per parts of saidcopolymer, and a source of polyvalent metal ion present in an amountchemically equivalent to about 0.5 to 2 times the carboxyl content ofsaid copolymer to provide 15 to 50 percent by weight of a polymericmetallocarboxylate elastomer; and from about 1 to 20 percent by weightplasticizer, heating the mixture, extruding and curing the mixture at atemperature above at least about room temperature and obtaining aflexible detonating fuse.

3. A process for manufacturing detonating fuse which comprisesintimately mixing a composition comprising 40 to 80 percent by weight ofa cap-sensitive particulate high explosive; a dispersion of a copolymerof from about 50 to 80 percent by weight of a butadiene, from about 10to 45 percent by weight of an acrylonitrile and a suflicient amount ofan acrylic acid to provide from about 0.001 to 0.3 carboxyl equivalentper 100 parts of said copolymer, and a source of polyvalent metal ionpresent in an amount chemically equivalent to about 0.5 to 2 times thecarboxyl content of said copolymer to provide 15 to 50 percent by weightof a polymeric metallocarboxylate elastomer; from about 1 to 20 percentby weight plasticizer; and up to about 25 percent by weight of apolyurethane elastomer, heating the mixture and extruding said mixturearound a reinforcing element substantially centrally positioned alongthe longitudinal axis of the fuse, and curing the mixture at atemperature above at least about roomtemperature and obtaining aflexible detonating fuse.

4. A process for manufacturing detonating fuse which comprisesintimately mixing a composition comprising 40 to 80 percent by weight ofa cap-sensitive particulate high explosive; a dispersion of a copolymerof about 50 to 80 percent by weight of a butadiene, from about 10 to 45percent by Weight of an acrylonitrile and a suflicient amount of'anacrylic acid to provide from about 0.001 to 0.3 carboxyl equivalents per100 parts of said copolymer, and a source of polyvalent metal ionpresent in an amount chemically equivalent to about 0.5 to 2 times thecarboxyl content of said copolymer to obtain 15 to 50 percent by weightof a polymericmetallocarboxylate elastomer; from about l to 20 percentby Weight plasticizer; up to about 25 percent by weight of apolyurethane elastomer, heating the mixture and extruding said mixturearound reinforcing yarn substantially centrally positioned along thelongitudinal axis of the fuse, and curing the extruded explosivecomposition at a temperature above at least about room temperature andobtaining a flexible detonating fuse.

5. A process for manufacturing detonating fuse which comprisesintimately mixing a composition comprising 40 to 80 percent by Weight ofthe cap-sensitive particulate high explosive pentaerythritoltetranitrate; an aqueous disperson of a copolymer of from about 50 to80percent by weight butadiene, from about to 45 percent by Weightacrylonitrile, a sufficient amount of methacrylic acid to provide fromabout 0.001 to 0.3 carboxyl eqiuvalent per 100 parts of said copolymer,and a source of polyvalent metal ion present in an amount chemicallyequivalent to about 0.5 to 2 times the carboxyl content of saidcopolymer to provide to 50 percent by weight of a polymericmetallocarboxylate elastomer; from about 1 to percent by weightplasticizer; up to about percent by Weight of a polyurethane elastomer,heating the mixture and extrud'mg said mixture around reinforcing nylonyarn substantially centrally positioned along the longitudinal axis ofthe fuse, and curing the extruded explosive composition at a temperatureabove at least about room temperature and obtaining a flexibledetonating fuse.

6. A process for manufacturing detonating fuse Wherein a firm bond isestablished between the reinforcing means and the explosive compositionwhich comprises intimately mixing a composition comprising 40 to 80percent by weight of a cap-sensitive particulate high explosive; anaqueous dispersion of a copolymer of from about 50 to 80 percent byweight butadiene, from about 10 to 45 percent by weight acrylonitrileand a suflicient amount of methacrylic acid to provide from about 0.001to 0.3 carboxyl equivalent per 100 parts of said copolymer, and a sourceof zinc ions present in an amount chemically equivalent to about 0.5 to2 times the carboxyl content of said copolymer to provide 15 to 50percent by Weight of a polymeric me'tallocarboxylate elastomer; fromabout 1 to 20 percent by weight plasticizer; up to about 25 percent byweight of a polyurethane elastomer, heating the mixture, and extrudingsaid mixture around reinforcing nylon yarn substantially centrallypositioned along the longitudinal axis of the fuse, and curing themixture at a temperature above at least about room temperature andobtaining a flexible detonating fuse.

7. A process for manufacturing reinforced detonating fuse wherein a firmbond is established between the reinforcing means and the explosivecomposition which comprises intimately mixing a composition comprisingto 80 percent "by weight of the cap-sensitive particulate high explosivepentaerythritol tetranitrate; an aqueous dispersion of a copolymer offrom about to percent by weight butadiene, from about 10 to 45 percentby weight acrylonitrile and a sufficient amount of methacrylic acid toprovide from about 0.001 to 0.3 carboxyl equivalent per parts by weightof said copolymer, and a source of zinc ions present in an amountchemically equivalent to about 0.5 to 2 times the carboxyl equivalentsof the copolymer to provide 15 to 50 percent by weight of a polymericmetallocarboxylate elastomer; from about 1 to 20 percent by weightplasticizer; up to about 25 percent by Weight of a polyether urethaneelastomer, heating the mixture to remove water and extruding saidmixture around reinforcing nylon yarn substantially centrally positionedalong the longitudinal axis of the fuse, and curing the formed mixtureat a temperature above at least about room temperature and obtaining aflexible detonating fuse.

References Cited UNITED STATES PATENTS 2,363,569 11/1944 Caldwell et a1.264---3 2,687,553 8/1954 Colombo 264-3 2,863,353 12/1958 Brimlcy 264-33,155,749 11/1964 Rossen et al. 264-3 L. DEWAYNE RUTLEDGE, PrimaryExaminer.

